1. Field of the Invention
The present invention relates to an architecture for a high volume printing system employing a number of print engines and the distribution of print jobs therebetween.
2. Description of the Prior Art
In recent years efforts have been made to enhance the speed, quality and versatility of printing text and other images, in black and white or in color, to match the capabilities of source image generators. The enhanced speed and other capabilities of source image generators, including mainframe computers, personal computers, computer workstations and CAD/CAM systems, document scanners, facsimile transmitters and receivers, high throughput copiers, and other more specialized graphic image processing and printing for forming composite color images from source images, e.g. the Kodak Premier Image Enhancement System available from Eastman Kodak Co., and for reproducing still photographic quality prints of video image frames, e.g. the Kodak SU6500 Color Video Printer available from Eastman Kodak Co., place ever increasing demands on "print engines" which print the images generated by these source image generators. Such print engines include laser beam printers, light emitting diode printers, liquid crystal shutter printers, ink jet printers and thermal printers.
Thermal dye transfer printers capable of printing high quality color images, as disclosed in U.S. Pat. No. 4,710,783 incorporated herein by reference, have recently been developed and employed in systems which include the above-listed source image generators. The source image generators are coupled to the print engine or engines through source image signal processors which provide an encoded data set through a data bus to a print engine controller of the type shown in FIGS. 5 and 6 of the '783 patent. Further image signal processors are disclosed in U.S. Pat. No(s). 4,941,108 and 4,999,654 where the source image from a host system is processed under the control of software operating a central processing unit to provide rasterized lines of digitized video data for each image field or page through a laser beam printer/video interface to a print engine.
Usually print engines are coupled to one or more source image generators, e.g. two or more personal computers, a local area network for a set of personal computers, or to a combined document scanner and facsimile machine, as shown, for example, in U.S. Pat. No. 4,947,345. In such systems, it is necessary to provide a queue management software process for prioritizing the printing of specific types of print jobs and to provide two-way communications between the print engine, the job SCHEDULER and the source image generator. In a simple FIFO queue management system each print job is assigned by the SCHEDULER to the print engine in the order received from the network bus and the print engine indicates when it is ready to commence and has completed printing a print job. In certain systems it is desireable to prioritize certain types of orders, e.g., facsimile over copying as per the '345 patent.
In certain, high volume printing systems, it has become necessary to couple more than one print engine to one or more source image generator through a single SCHEDULER and an image processor associated with each print engine to distribute print jobs in the FIFO basis among available print engines that are capable of printing the specific job (i.e., are loaded with the appropriate size medium, are capable of color printing, etc.).
This architecture includes a connection to the source image generator by an incoming data bus BUS1. Data files pass through BUS1 to a SCHEDULER computer, which interrogates data files received through BUS1 to determine if any print engine PEm is capable of printing the data file. If a print engine PEm is capable of printing the file and an image processor, IPl-IPn, is available, the data is passed through a network bus BUS2 to the appropriate image processor, IPm. The image processor, IPm, applies one or more computer algorithms to the data file creating the rasterized image to be printed by the print engine, PEm. The print engine, PEm, will print one or more copies of the image as requested with the data file. The system throughput, measured in copies per hour, depends upon maximizing the probability of rasterized images being available and ready for printing by the print engines, PEl-PEn.
The connection of a single image processor, IPm, to a single print engine, PEm, through the interconnect bus, BUSpm, prevents multiple copies of an image to be printed by other available print engines, PEl-PEn. The image processor, IPm, is only capable of preparing images for the print engine, PEm, until it has filled its buffers. The system performance is therefore reduced by limiting the access of an image process, IPm, to only one print engine, PEm.